Folder reed switches



Nov. 17, 1970 J. T. L. BROWN FOLDER REED SWITCHES Filed Dec. 21, 1967 FIG.

& 7/11/1120 FIG. 4

INVENTOR J. 7? L. BROWN ATTORNE United States Patent US. Cl. 335-154 3 Claims ABSTRACT OF THE DISCLOSURE A reed switch wherein at least one blade is disposed in a housing and has a portion folded over longitudinally at least one time to form a free end portion of at least a double thickness which is operable to close a magnetic gap.

The applicant, in whose name this application was prepared, has devised an improved armature particularly for glass sealed switches where the parts of the relay are necessarily small.

This application is based on the use of a configuration which provides the necessary compliance of an armature in a glass sealed magnetic switch in a single thickness of a flattened section, but which, by folding over the single thickness on itself, provides in the same piece an effective magnetic cross section of twice the thickness. A will be shown, the principle can be applied in a large variety of types to obtain improved performance Without increase in overall size.

An important feature of the design is the use of progressive compression between rolls instead of stamping, to produce the flattened section from wire. Because of the displacement of the material along the wire axis that is involved in rolling, better dimensional control and longer tool life are obtained. The advantage is specially important where, as in these applications, the flattened section is relatively long. The ratio of the initial wire cross sectional area to that of the flattened section is greater than that obtained by stamping. Among other things, this provides a means for identifying the flattening method that was used.

Reference is now made to the accompanying drawings for a better understanding of the nature and objects of the folded reed switches of the present invention, which drawings illustrate the best mode presently contemplated for carrying out the objects of the invention and its principles, and are not to be construed as restrictions or limitations on its scope. In the drawings:

FIG. 1 is a front elevational view of a blade forming the reed switch of the present invention;

FIG. 1A is a transverse sectional view taken along the line 1A-1A of FIG. 1;

FIG. 2 is a front elevational view, partially in section, depicting an embodiment of the reed switch of the present invention;

FIGS. 3-5 are views similar to FIG. 2, but showing alternate embodiments of the present invention; and

FIG. 5A is a transverse sectional view taken along the line 5A5A of FIG. 5.

FIG. 1 shows an armature made in this way and FIG. 1A is a cross sectional view of the same indicating that the original material has a circular cross section, such as a wire. FIG. 2 shows a pair of armatures 1 and 2 mounted in the same container and cooperating with each other. The cantilever section of the armatures of FIG. 2 are formed from a double length of the flattened material folded over. As the compliance is inversely proportional to the thickness, this reed has eight times the compliance of a single reed with the same magnetic cross section; or twice the magnetic cross section, or four times the magnetic force capability of a reed made from a single thickness.

FIG. 3 shows a switch with a single folded armature 4, which makes a normally closed contact with a non-magnetic back contact 5, and a normally open contact with a magnetic pole piece 3. An important characteristic of this back contact element is that it is supported by resting against the glass 6, directly behind the point of contact with the armature. The point at which it rests against the armature is not necessarily directly opposite the magnetic contact. Instead, it is at a point further down which is empirically selected to produce a minimum of bounce.

The doubled-over armature has a distinct advantage from the standpoint of contact bounce. This is primarily because the impact energy at the contact is quickly dissipated by an induced series of impacts which Occur between the reeds at the end away from the contact. Advantage of this kind is obtained with contact on both sides of the double reed, but indications are that contact on the side away from the free reed is preferable. For this reason, the preferred configuration is shown on the back contact in FIG. 3.

FIG. 4 shows a modification of FIG. 3 which employs three bends in the flattened section 7. This provides three single thickness sections which contribute to the compliance. The two sections 7a and 711 at the base form a pole piece and the two sections 7c and 7d at the tip form an armature, both having a magnetic thickness corresponding to two single thicknesses. A primary magnetic gap 8 and an auxiliary magnetic gap 9 are thus formed. The auxiliary magnetic gap 9 in this switch is a novel one-piece construction. As the eifective cross-section on each side is increased by adding folded sections, operation is practicable when the connecting section, which shunts the gap, approaches magnetic saturation.

An important feature of this type of construction is that the magnetic gap 8 which also provides the electrical contact always closes first. The auxiliary gap 9 on the folded combination then closes, increasing the contact force at the electrical contact and providing a double seat for the armature section that minimizes chatter. When the switch opens, the auxiliary gap 9 always opens first, thus contributing to the velocity with which the electrical contact opens.

FIG. 5 shows a switch in which the armatures 7 and 10 are made from a pile up of four sections. The working gap is at the folded tip away from the base. All three of the sections nearest to the base contribute to the compliance.

The two reed sections at the contact have similar mechanical and magnetic characteristics to the double reed of FIG. 2. The two sections near the base provide a number of additional important advantages. They contribute to the effective magnetic pull in the gap by carrying part of the magnetic flux. In particular, they carry the leakage flux that otherwise would enter the moving reed on the side away from the contact. Also, the small reverse force which would otherwise exert on both sides of the armature is present only on the aiding side. This latter force is usually described as repulsion.

When the switch closes, the impact energy can be dissipated, as described above, by friction and by induced impacts which take place between the reed sections away from the gap. On release, the usual undamped oscillation is very eifectively snubbed by impact at the tip against the adjacent reeds.

In all of the above cases where the thickness of the flattened section is made less than that of a reed that it replaces, the force that the reed can withstand at its tip is reduced. A proposed general way to compensatefor this is to use an alloy for the reeds that has a larger tensile strength in the annealed conditionv than is necessary for glass sealing.

The proposed alloy contains iron, nickel and cobalt, 'with substantially no trace elements. Its thermal expansion characteristics can be made equivalent to that of the iron-nickel alloy now generally used by using about the same iron content. Its tensile strength will increase with cobalt content to the point where it becomes unworkable without the use of additions like vanadium. Such additions are undesirable as they complicate the problem of producing a contact surface free from oxide.

Along with the increase in tensile strength is an increase in coercive force. This can be objectionable where differential sensitivity rather than load handling capacity is important. It can be of marked advantage in cases where the switches are to be used in latching relays.

The surface of both of these alloys is not ideally adapted to electrical contact use, so that some kind of surface treatment is usually desirable. In many cases the surface treatment results in a non-magnetic shim on the contact which defeats part of its purpose by reducing the magnetic contact force available.

To reduce this disadvantage, it is proposed to apply a sintered coating made up of particles of magnetic material along with particles of a material selected for its electrical capabilities. The most important type of contact material would be one like tungsten or tungsten carbide, used to provide resistance to erosion rather than low resistance. This is because low resistance contacts can usually be obtained by diffusing materials like gold or palladium into the reed surface to form a magnetic alloy.

The magnetic material should preferably be an element, like iron, nickel or cobalt, to provide low resistance. Of these, cobalt appears to be preferred. In addition to good magnetic resistance characteristics, it has molecular characteristics that tend to avoid sticking (see Mason Pat. 3,146,328). Because of its lower melting point, it can be used as the binding agent in the sintered mixture.

. defining an additional magnetic gap with one of said portions of a double thickness.

2. The switch of claim 1 wherein said base portion has a cross sectional area at least 30% greater than that of said armature portion.

3. The switch of claim 1 wherein said means defining an additional magnetic gap comprises a pole piece fixed within said housing.

References Cited UNITED STATES PATENTS 3,075,281 1/1963 Spooner.

3,171,190 3/1965 Zimmer 335-154 X 3,236,965 2/1966 Dal Bianco et a1. 335-454 X FOREIGN PATENTS 1,126,032 3/ 1962 Germany.

1,467,763 12/ 1966 France.

OTHER REFERENCES IBM Technical Disclosure Bulletin, Reed Switch, F. J. Soychak, vol. 5, No. 3, August 1962.

Ferromagnetism, R. M. Bozorth, 1951, page 160.

BERNARD A. GILHEANY, Primary Examiner R. N. ENVALL, JR., Assistant Examiner US. Cl. X.R. 

